package com.dreem.singleton.type6;

/**
 * @program: DesignParrtern
 * @description: 双重检查
 * @author: Peng
 * @create: 2021-01-22  11:30
 **/
public class SingletonTest06 {
    public static void main(String[] args){
        System.out.println("双重检查，volatile");
        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();
        System.out.println(instance1 == instance2);
        System.out.println("instance1的hashcode() = " + instance1.hashCode());
        System.out.println("instance2的hashcode() = " + instance2.hashCode());
    }
}

// 双重检查
class Singleton{
    private static volatile Singleton instance;
    private Singleton(){}

    // 提供一个静态的公有方法，加入双重检查代码，解决线程安全问题，同时解决懒加载问题
    public static Singleton getInstance(){
        if(instance == null){
            synchronized (Singleton.class){
                if (instance == null){
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}
